Metallurgical furnace



Jam@ 14, 1932. E, H BUNCE ET AL 1,863,185

METALLURG I CAL FURNACE Filed March 24, 1950 INVEN OR I Wmv-s ATTORNEYPatented dune 14, 1932 Unirse stares EELH. BU'NCE, CLARENCE J. LENIZANDGEORGE T. MAHLER, 0F PALMERTON, :PENN- SYLVANIA, ASSIGNQRS TO THE NEWJERSEY ZINC COMPANY, OF NE'W RK, N. Y.,

CQRPGRTION OF NEW JERSEY METALLURGICAL FURNACE This invention relates tometallurgical Jfur-l heated reduction furnaces, such as are employed inthe reduction of zinci'ferous `materials.

lt has heretoore been proposed to build-up externally heated chambers orretorts for the v1.0 reduction of zinciferous material with amultiplicity of pieces vof temperature-resistant material of goodheat-conducting qualities. The pieces of temperature-resistant materialusually consist of refractory material,

35 such as vdensely pressed silicon'carbide bricks,

copatentee.

whichare carefully assembled to form a rsuhstantially Zinc-vapor-tightchamber. Such a huilt-up retort is disclosed in United States Patent No.1,680,726, of which one of us is a The patent more particularlydiscloses a vertically disposed and externally heated retort huilt-up ota multiplicity of suitable refractory' brick fitted together with plainbutt joints. Charge materials in 5 the form of agglomerates areprogressively passed downwardly through the retort asthe zinc reductionstep proceeds to completion. While such built-up retorts are a markedimprovement over the monolithic and built-up retorts heretoforeemployed, in time they tend to rupture. This rupturing of the retortstakes place more particularly in 'their upper sections.r Considerabletime, labor and expense are involved in repairing or re-buildin suchruptured retorts.

When employing a retort such as that disclosed in 'the above mentionedpatent in the reduction of zinoiferous material, it is customary tomaintain a temperature of anorexi- 40 mately 1250o C. throughout theheightl hf the 4.5 per end of the retort and they become hotter heatingchamber. Since the charge materials .are progressively passed throughthe retort, as the reduction step proceeds to completion, theagglomerates are relatively cool in lthe up and hotter as they proceedthrough the retort. ,An externally applied temperature of approximately1250" C., in the case of some zinc ores at least, seems necessary inorder to drive suliicent heat into the core of the charge vset up toremove or eliminate the last traces of available zinc. This means thattoward the end of the reduction process the charge materials will thushave risen to a temperature of close to 1250o C.

in the case of the charge materials confined in the upper section of theretort, it is to be noted that the cool charge takes on heat rapidly,thus tending quickly to ahstract a very large amount oi heat away 'fromthe inner face ofthe retort walls. As the heating operation continues,the agglomerates next to the inner retort walls gradually reach theirtemperature of reduction. The agglomerates close to the inner retortWalls are soon suliicientlyheated to reach their temperature ofreduction. rThe resulting zinc reduction step is itself an endothermicreacmately 12500 C.) and the inside of the retort walls at its uppersection (approximately OGOO C), numerous stresses and strains are' inthe retort walls, which are proportional to the temperaturediiierential, between the inside and the outside of the Walls. Thesestresses and strains intime tend 'to rupture the retort walls.

A different situation, however, exists in the lower section of theretort. By the time 'the agglomerated' charge materials have reached thelower section of the retort the reduction step itself will have proceedto, or almost to, completion. Since these agglomerates have beensubjected to continuous heat- ,ing during their passage from the upperend to the lower end of the retort, the are no longer relatively, cooland have ta (en on a temperature substantially equal to that maintainedat the outside of the retort walls. Furthermore,l since the reductionreaction has gone to substantial completion, `further amounts o heat arenot taken up to el'eet the reduction reaction.

lIn other words, the charge materials confined in the lower section ofthe retort may be regarded as a substantially inactive or dead load thatfinally attains a temperature substantially equal to that provided onthe inv G bebuilt in a. single section, itis readily sub- `lower end ofthe retort.

side of the retort walls. The spent charge materials adjacent to theinside ofthe retort Vwalls thus serve to take 11p-the temperature shockthat the inner walls of the retort are normally subjected to when freshcharge inan terials are being heated. This means 'that there is lesstemperature differential between the inside and thev `outside of thewalls of the lt therefore follows that stresses and strains are notreadily set up in the walls of the lower retort section, and thereforethey are not as susceptible to rupture as are the .walls of the upperretort section. y

In copend'ing application, Serial. No. M8,- 914, filed February 17,1927, there is disclosed an apparatus for smelting zinc coinprisin avertically disposed metal retort adapted for external heating., Thecharge materials, preferably in an agglomerated form, may beprogressively passed downwardly through the retort as the reductionoperation proceeds to completion. Metal retorts offer a number ofdesirable advantages; especially over relarge quantities of heat matorts built-up of refractory bricks. In the first place, a metal retortmay have a wall of less thickness than that of a refractorybrick/retort, therefore a considerable amount of heatmay more readily bepassed through the. walls of such a metal retort and into the chargematerials' confined therein', vand thus the temperature differentialbetween the outside an the inside of the metal retort walls is very low.A s va consequence, less heat is required in the surrounding heatingchamber to hold a given temperature within a metal retort. This meansthat a metal retort may be heated with less fuel consumption than instituted as a unit -for one that has failed. In the case of a refractorybrick retort, on the other hand, considerable time is required to teardown an old retort and .build up a new one. l t

Metals and alloys are well adapted to with stand the heat shocksproduced by the in# sertion of' fresh batches of charge into the top ofa verticle zinc retort of the type discussed here. The fresh charge atthe top of the retort since the reaction between zinc oxide and carboninthe charge is endothermic, acts as a cooling agent and tends to keep thetop of a metal retort from reaching a temperature at which it wouldsoften to a dangerous de fictitious.

nasales degree ofheat. In the case of refractory retorts, the reverse istrue: a refractory retort huilt of appropriate materials 'willstand thehigh bottom temperature to which it is subjected on account of theprogressive elimination of Zinc from the charac better than the.

heat shocks produced at the top by the in sert-ion of fresh cha-nge;l

A. study of reducing operations conducted within a.vertically disposedand externally heated retort shows that `the ideal retort would be oneconstructed of materials which will at its top section deliver to theinside wall of the retort a large quantity of heat somewhat above thetemperature of reduction (950 C.) with the least possible heatdiderential across the thickness of the retort wall, ai1d which will, asthe charge moves downwardly, deliver at thelinside wall of the retortthe desired quantity of heat at a gradually 'increasing temperature;until at the lower section of the retort the inside wall temperatureapproximates 12500 C. l'hese 4conditions require that the heatingchamber of the furnace be constructed or equipped Vwith devices capableof controlling the conibustion of fuel so that ythe heating chambertemperature rises from that required to deliver an inside walltemperature somewhat above 950 C. at the top section to an inside retortwall temperature of about 1250" C. at

the lower section of the retort,

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As a result of our investigations, we have ideal operating conditionsjust enumerated.

A combination retort has been developed which for the most partsatisfies these speci- In the case of a vertically disposed andexternally heated retort, we have found that avmetal upper section ofsuitable construction may advantageously be employed which willwithstand temperatures of at least 1000O C, in a reducing atmosphere onthe inside of the retort, and in a reducing or oxidizing atmosphere onthe outside of the retort for a relatively long period of time withoutfailure. l The lower section of the retort is constructed of suitableheat refractory material, such as brick, which will withstand atemperature 'of 1250 C. in the same atmosphere for a relatively longperiod of time without failure. We have also found that a oint may beprovided between the refractory section and the metal section of theretort that is substantially zinc-vapor-tigbt.

Our invention therefore contemplates a metallurgical furnace comprisingan externally heated reduction retort built-up in part of refractorymaterial and in part of metal.,

In the present preferred practice of the in- Vention, the metallurgicalfurnace is provided with a vertically dispose-d and externally heatedreduction retort, the lower section of which built up of a multiplicityof pieces of suitable heat refractory brick of good heat-conductingqualities, while the upper section is constructed of suitable metal,preferably an alloy, adapted to withstand the prevailing temperaturesand atmospheres. A joint is provided bet-Ween the refractory bricksection and the metal section that `is substantially zinc-vapor-tight.The retort is centrally disposed within an appropriate heating chamber.Suitable fuel may be introduced into and burned within the heatingchamber to provide the 'desired temperatures and quantities of heat.

When operating the metallurgical furnace of the invention in thereduction of Zinciferyous materials, the heating chamber of the furnaceis maintained at a temperature gradient of approximately 12500 C. at itslower end and about 10000 @-10509 C. at its upper end. Thus, thetemperature at the bottom ofthe refractory brick retort may bemaintained around 1250O C. The temperature at the joint between therefractory and metal sections of the retort is maintained atapproximately 1100o C., and the temperature around the upper sect-ion ofthe metal retort is maintained at about 1000l050 C.

The gradual increase in the heating chamber temperature from the top tothe bottom I of the retort may be brought about by the 5 burning ofthefuel at the bottom of the heating chamber and cooling the products ofcombustion as they rise toward the top of the heating chamber. Thus, thehot combustion gases may be cooled by introducing a cooling agent, suchas steam or air, into the central and/or upper sections ot the heatingcham- 0r, in utilizing a down-drop, the combustion fuel may beintroduced at or near the top'of the main heating chamber, and air maybeintroduced at various points throughout the height of the chamber toregulate the combustion of the fuel to give the de sired temperaturegradient; or, a separate DQ heating chamber may be provided for eachretort section.

The novel features of the present invention, it is believed, will bebetter understood by J Fig. 2 is an enlarged sectional detail of atelescoping joint shown in Fig. 1.

The apparatus shown comprises a main furnace structure l0 resting ouconcrete foundations 1l. The furnace structure comprises 3") a bottom12, side walls 13 and an arched roof reference to the accompanyingdrawing, tak-` en in conjunction with the following descrip- 14Cconstructed of suitable refractory material, such as heat-resistantbrick. These furnace linings (define a heating chamber 15.

A suitable number of ports 16 and 17, eX- tending completely through theside walls of the furnace structure are appropriately spaced throughoutthe height of the furnace structure. These ports are adapted to receiveair and fuel, such as pulverized coal, oil, gas, etc., which may beburned within the heating chamber. Electrical energy may also beemployed appropriately to heat the furnace and to eli'rct the desiredreduction operation. Une or more port-s are preferably provided at ornear the lower section and at or near the middle of the heating chamber.in outlet 18 is provided at or 'near the upper end ofthe heating chamberfor the withdrawal of heating gases. This out-let preferably connectswith a stack or chimney (not shown).

A number of relatively small openings 19 are Iprovided through the sidewalls of the furnace structure at spaced intervals throughout the heightof the heating chamber for the taking of pyrometric readings. An outermetallic casing 20 completely surrounds the main furnace struct-ure. Thespace between. the top of the metallic casing and the arched Iroof isfilled with suitable heat-insulating material 21, such as diatomaceousearth.

A. lvertically disposed retort extends centrally of and completelythrough the heating chamber. The retort shown comprises two connectingsections, a lower section 22 constructed of suitable refractorymaterial, such as refractory brick, and an upper section 23 constructedof suitable metal, such as an alloy, that is adapted to withstandprevailing temperature and atmospheric conditions. lt is important thatthe two sections of the rctort be joined hermetically. That is to say,the joint between the two sections should be substantiallyzinc-vapor-tight. Moreover, the joint should be sufficiently tight toprevent retort gases from escaping into the heating chamber, or heatinggases in the heating chamber from scoping` into the retort.

ln the construction shown in the drawing, the lower end of the upper(metal) section is flared out to form a lip, shoulder or flange 2li.This flanged section forms a base for the support of the metal sectionof the retort. A. suitable connector casting 25 is placed between theupper end of the lower retort (refractory) section and the lower end ofthe upper section. This connector casting base is circular in plan, withan opening in the center to conform to the configuration of theadjoining retort sections, and 'lA-shaped in crosssection. The lowerhalf of the casting embraces the top of the refractory retort sectionand rests thereon. An intervening layer of silicon carbide fines ispreferably provided on the upper face 26 of the refractory retortsection, so that the casting may be non-leakably 5 of the refractoryretort section, in order to provide as far as possible a non-leaking oint.

The upper half of the connector casting.

serves to receive the flanged portion'of the lower end of the uppermetal retort section. The space 27 between the outer wall of the end ofthe metal retort and the inner upper portion o f the connector castingring is filled with silicon carbide fines, sand or similar material toact as a seal. y

Batlle walls 28 are advantageously built into the side walls ofthefurnace structure. These bailles extend laterally across the heatingchamber and are so positioned with respect to the ports located aboutIridway up the heating chamber that heating gases or fuel introducedtherethrough may be deviateed from and `kept substantially out ofimmediate Contact with the retort. The ports in question are shown inthe side walls of the furnace substantially on the same level as thejoint between the upper and lower sections of the retort. The baiiiesare advantageously placed close to the joint in order to protect thesame from direct contact with heating gases at their hottest zoneintroduced through the immediate ports. In fact, steam and/'or airmay beintroduced through these ports to cool the heating gases thus protectingthe metal retort section against over-heating.

Similar protecting baffles 29 are constructed in the bottom of thefurnace in order to protect the lower retort section from immediatecontact with combustion gases resulting from the burning of fuelintroduced through the lower ports. fThe Vbailles may of course likewisebe fastened into the side walls, or a combination of the two types ofconstructionmay be employed.

While the retort, or its sections, mav have any desired configuration,in the present preferred practice of the invention the retort iscircular in outline, having an internal diameter of 15%E inches. Thepassageways of both sections of the retort are in substantial alignmentwith one another. ln order that the retort may expand and contractindependent of the furnace structure, it is preferred that the retort besupported by the In the present instance, the lower section of therefractory retort is supported by the botfurnace structure at not morethan one point.y

height of 9 feet 11 inches, and the metal retort section has an overallheight of 10 feet 1 inch.

The lower end of the refractory retort section terminates with a sleevemember 30 which acts as an extension thereof. This sleeve is attached tothe underside of the bottom of the furnace structure, and its passagewayis in substantial alignmentwith the passageway of the retort. Arevolvingplatform 31, moving about a vertical axis 32, is locatedA immediatelybelow the lower end of the retort and sleeve. It is adapted to receivespent residues or agglomerates 33 and 'to discharge them as the platformisl revolved. l The upper end of/the metal retort section -movablconnectswith a metal prolongation 34, which may be constructed 0fwrought iron, into which the metal retort section advantageouslytelescopes (see 2), This metal prolongation preferably extends aconvenient distance above the furnace structure.

The telescoping joint provided between the l upper end of the metalretort section and the metal prolongation comprises an annular band 35of'flat iron, 21/2 inches wide by l@ inch thick, riveted along theinside of the lower end of the metal prolongation. The inside diameterof the annular band is suf- `icien'tly large to permit of the entry ofthe metal retort section, so that any expansion or contraction of themetal retort section may easily take place within the fixed metal pro.

longation. One or more layers of asbestos wick packing 36 are snuglyfitted into the space provided between the upper periphery vwhich restsan eliminator structure B9 adapted to support and contain an eliminator40. This eliminator structure comprises an outer metallic casing /llthat completely surrounds the eliminator, leaving a space adapted toreceive heat-insulating material 42, such as coal dust. One or moredoors e3 are provided at or near the lower end of the metal casing forthe'remcval of dust coal in order to regulate thetemperature of theeliminator during reduction operations. The outermetallic casing may beof any size adapted to give an intervening layer of heat-insulatingmaterial of desired thickness. The metal casing is preferably open atIthe top, or has an opening at or'near the top, for the introduction ofheat-insulating material.

.A base plate 44 rests on the I-beams, which is adapted to support theeliminator struc- 'fractory material, such as heat-resistant brick.These brick are preferablv of the same general type as that employed inthe building-up of the eliminator, i. e., silicon carbidey brick. Thedesired telescoping elfect may be obtained by arranging the joint brickin the form of inverted steps, as shown in the drawing.

It will be seen that the telescoping joint may be so constructed astoyprovide an eliminator of any desired cross-sectional configuration;The brick going into the joint are advantageously kept in alignment bymeans of a circumferential steel band 47.

An olf-take pipe 48 is provided at or near the upper end of theeliminator forthe withdrawal of zinc vapor and retort gases. Itcommunicates with a zinc vapor treatment device 49. If zinc metal is tobe produced, this device consists of a condenser. If, on the otherhand,zinc oxide is to be manufactured, the device is one adapted toeil'ect the oxidation of the incoming zinc vapor. In the case of themanufacture of zinc dust, the device consists of a canister designed forthe condensation of the zinc vapor into minute zinc particles.

Tlie upper end of the eliminator is provided with a charge feedin gdevice 50 that extends downwardly in the eliminator to a distanceslightly below the gas and vapor olftake pipe, so that charge materials51 may be kept therefrom; thus leaving a free passageway to and throughthe .olf-take pipe. A removable cap 52 lits over the mouth of thecharging device.

The above described apparatus may be operated as follows in thereduction of zinciferous material, and more particularly with respect tozinciferous material containing objectionable amounts of lead and thelike:

The cap 52`is removed and an appro riately agglomerated charge of mixedzinclferous material and oarbonaceous reducing agent is` fedinto thecharging device 50. A suiiicient amount of the agglomerates are thusintroduced until the communicating passageways yof the retortsections,the eliminator and the charging device itself are substantially lilled.The cap 52 is then returned.

Air and fuel, such as oil, are introduced Se through the ports 16 and17.' As the combustion gases circulate around both the lower and upperretort sections, spent gases ultimately iind their way through theopening 18 and into the stacker chimney (not shown).

53 The highly heated combustion gases formed by the fuel introducedthrough the lower ports 16 strike the baille walls 29, kthus protectingthe retort section 22 from immediate contact therewith. In a similarmanner, the baiie walls 28 protect the joint between the lower and upperretort sections from immediate contact with the combustion gasesresulting from fuel introduced through the ports 19.

Pyrometric temperature readings are periodically or continuously takenthrough the openings 19. Temperature conditions within the heatingchamber are suitably regulated in accordance with the temperaturegradients to be maintained.' In order to have a temperature gradientincreasing from the upper end of the heatingl chamber to the lower endofthe heating chamber, the hottest gases are preferably introducedthrough the ower ports. Asthe heating gases rise upwardly through theheating chamber, while swirling around the retort, they are graduallycooled. If additional cooling effects are desired, steam and/or air maybe suitably introduced at various points ythroughout the height of theheating chamber. Thus, steam may advantageously be introduced throughthe ports 19. The relatively cooler steam contacts with the risingheated gases and tends effectively to lower their temperature. A coolingmedium may also advantageously be introduced through openings 19, orsimilar openings provided in the side walls of the furnace structure forthat purpose. As 100 pointed out above, it is preferred to maintain atemperature of approximately 1250 C. in the lower part of the heatingchamber, and a temperature of approximately 1000-1050 C. in the upperend of the heatchamber.

The heat externally applied to both the lower and upper sections of theretort is ultimately driven through the retort walls and into the chargeconlined therein. Since the upper metal retort section has a relatively'thin wall, heat is readily transferred through its vwalls into thecharge. As pointed out above, under ideal operating conditions it ispreferred to have large quantities of heat transferred to the chargematerials in the upper section of the retort. This desirable result isobtained with the metal retort section, while yielding a relativelysmall temperature diiierential between its outer and inner wall surface.On the other hand, it is also preferred to deliver the desired amount ofheat into the charge materials in the lower end of the retort atincreasing temperatures. This advantageous result is obtained whenemploying a lower retort section constructed of refractory brick, thewalls ci which are suciently thick to withstand the elevatedtemperature.

When the charge materials confined within the retort are heated to theirtemperature of reduction, zinc vapor is liberated and retort` gases areevolved. Due to the natural buoyancy of the hot vapor and gases, theyVtend to rise upwardly. rIhis upward movement ofthe vapor and gases ispreferably assisted by providing and maintaining a stack draftthroughout the system. For this purpose, it is advantageous to have aretort of substantial height. Moreover, in the preferred practice of theinvention, regulated amounts of gases, such as air, are admitted intothe lower end of the retort.

As reduction proceeds to completion, the spent residues or agglomerates33 are removed from the lower end of the retort by setting the revolvingplatform 31 in motion. The movement of the platform tends to withdrawspent residues. As fast as spent residues are removed, the inner columnof agglomerates within the retort section tends to lower itself. thuseffecting a progressive movement of theagglomerates downwardly throughtheretort. The cap 52 is again removed and further amounts of freshcharge materials are introduced into the charging device, to compensatefor the spent residues that have been withdrawn from the lower end ofthe retort. If the process is to be operated substantially continuously,the cap may be removed and connection made with a source of materialadapted to feed fresh agglomerates into the system as fast as spentresidues are removed therefrom.

The liberated zinc vapor and evolved retort gases rise upwardly throughthe passageways of the retort sections, as agglornorates movedownwardly. rlhe mixture of zinc vapor and retort gases ultimately findsits way into the eliminator 40, where it contacts with the hot body ofagglomerates confined therein, and which agglomerates are aboutto besubjected to the reduction operation.

If the zinc vapor is contaminated with objectionable amounts of lead,dust, or the like, and it is desired to eliminate the same. thetemperature of the agglomerates confined i within the eliminator must becarefully controlled. ln other words, under appropriate temperatureconditions, the hot agglomerates confined within the eliminator areadapted to filter out the lead and dust without undue condensation ofzinc vapor, while permitting the purified vapor to pass on. If thetemperature of the agglomerates is too hot, provision should be made forremoving the excess heat. This may be accomplished by lowering'theamount of heat-insulating material 42 in the metal casing al. Coal dustmay readily be removed from the door or doors 43. On the other hand, ifthe agglomerates are not suficiently hot to avoid the condensationof-appreciable amounts of zinc vapor, additional heat-insulatingmaterial should be provided around the eliminator to inhibit dissipationof heat. This result may be accom- Lacasse fect the oxidation of theZinc vapor. Fur` thermore, if zinc dust is to be made, the deviceconsists of a canister adapted to condense theincoming zinc vapor intominute particles of zinc. v

A consideration ofthe structural features of the abovedescribedvapparatus will readily indicate that the metallurgical furnaceof the invention is 'peculiarly adapted for the reduction of zinciferousmaterials. The relative advantages and disadvantages of refractoryretorts and of metal retorts lare so balanced against one another in thecombined retort of the invention that the old disadvantages areminimized while practically all of the advantages of both types ofconstruction are retained.

We claim:

1. An apparatus for the reduction' of zinciferous material comprising avertically disposed and externally heated reduction retort, the lowersection being built-up of a multiplicity -ofrefractory brick, the uppersection being formed of suitable metal, the two sections being joined byan intervening casting vadapted to make a substantially zinc-vapor-tightjoint..-

2. An apparatus according to claim l, in which the upper end of themetal retort section movably connects with a fixed 'metal prolongation.

3. An apparatus according to claim l, in which the upper end of themetal retort section telescopes into a fixed metal prolonga-` tionwhereby expansion and contraction of the metal retort may freely takeplace within the metal prolongation.

4.A.n apparatus according to claim 1, in which the intervening castingis T-shaped in cross-section so that the lower half of the castingembraces the top lof the refractory retort section and rests thereon,and so that the upper half of the casting supports a ianged portion ofthe lower end of the metal retort section.

'5. An apparatus according to claim l, in which the joints between theretort sections and the intervening casting 'are sealed with anappropriate agent.

ln testimony whereofwe aiiix our signatures. l

EARL H. BUNCE. CLARENCE J. LENTZ. GEGRGE T. MAHLER.

EGG

